The Hypersonic Flight In the Turbulent Stratosphere (HYFLITS) research team was formed in 2016 and is currently funded by the AFOSR's Multidisciplinary Research Program of the University Research Initiative (MURI) grant, "Integrated Measurement and Modeling Characterization of Stratospheric Turbulence," awarded by the AFOSR’s High-Speed Aerodynamics Research Area in December 2017.
The multidisciplinary HYFLITS team is composed of experts in the fields of in-situ atmospheric measurements and analysis, atmospheric modeling and forecasting, and aerothermodynamics and aero-optical modeling. Our goal is to ask and resolve questions related to how future hypersonic vehicle designs can account for the effects of ambient atmospheric turbulence and particles in the middle stratosphere.
Identify and quantify the dynamics accounting for stratospheric turbulence sources, characteristics, intensities, and their statistical dependence on the meteorology below
Resolve uncertainties regarding small- and larger-scale turbulence impacts on hypersonic vehicle boundary layers and aero-optical systems
Establish critical particle concentration levels that may drive transition to turbulence in hypersonic boundary layers
Define the methodologies required for comprehensive, measurement- and physics-based, stratospheric turbulence forecasting, including a “strawman” forecasting system design
OBJECTIVE: Use high-altitude balloons for in-situ measurements to characterize turbulent velocity, temperature fluctuations, and particulate concentration and size distribution in upper stratosphere.
Balloon Bus Performance (ERAU)
Evaluating 2-balloon solution; descent comparable to IAP flights
Communication link to 170 km, 6-h flight
Particle Detector Deployment (UMN)
Focused on Alphasense particulate sensor
Calibrated in UMN Particle Technology Lab
Balloon Flights (UMN)
10 flights to date; more scheduled for Fall 2018
Developing reliable approach to reach 35+ km, descend slowly
Double-balloon with cutaway is current best approach
HASP Balloon Flight (UMN)
Alphasense sensor flown on NASA HASP
Obtained 9 hours of data at 125 kft (38 km)
Working to obtain calibrated particulate counts
Plan to fly more sophisticated payload on next year's flight
Fine-Wire Probe Development (CU)
Bandwidth increase for hotwire (velocity), coldwire (temperature) with constant-temperature control method
Adjustable gain/excitation for in-flight density variations
Prototype testing for LITOS comparison, Nov 2018
Initial construction completed Sep 2018
First calibration experiments in Nov 2018
OBJECTIVE: CFD for multi-scale modeling of gravity waves coupled with high-resolution simulations of instabilities and small-scale turbulence -- "Sources to Turbulence"
Atmospheric Deep Compressible Model (ERA)
Atmospheric Spectral Model (ERAU)
Computational Aerothermodynamics (UMN)
Our MURI effort includes close links between measurements, modeling, and theory to achieve the most comprehensive understanding of the dynamics underlying stratospheric turbulence, the impacts of turbulence and particles on hypersonic vehicle boundary layer stability, and turbulence influences on aero-optic propagation. Model results will contribute to specification of routine and focused measurement capabilities and strategies; evolving measurements will help guide new modeling studies; and current and new modeling results will be used as inputs to evaluate turbulence impacts on vehicle boundary layer stability and aero-optic propagation. A flow chart showing the expected links among program elements is shown below:
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